Recent progress of scientific and medical technologies, and newly developed medicines such as antibiotics and chemicals have enabled the treatment of various diseases heretofore considered to be difficult to treat. On the other hand, especially in developed countries where people are accustomed in such medical civilization, immunological resistance of human beings have lowered, and many people have suffered from various diseases caused by substances or microorganisms which heretofore had not hurt human beings.
Among what are referred to as diseases, microorganism examinations are essential for the treatment of diseases caused by microorganisms such as bacteria, viruses, or protozoa, to find their pathogens, to clarify their types, and to determine drugs to which they are sensitive.
At present, in the first stage of microorganism examinations, since the cause of a disease and the type of the pathogen can be estimated from the symptoms, various specimens, such as blood, are selected depending on the type of the disease, pathogens present in the specimens are morphologically identified, or antigens or the specific metabolites of pathogens (e.g., toxins or enzymes, etc.) existing in the specimens are immunochemically identified. This process is smear, tinction, or microscopy used in bacterial examinations, and in recent years, instantaneous identification has become possible in this stage by fluorescent antibody tinction or enzymatic antibody tinction.
Furthermore, the virus serological test, recently used in the detection of viruses, is a method for proving the presence of specific immunity antibodies that appear in the serum of a patient. Examples of the method include the complement fixation reaction in which the presence of antibodies or antigens is determined by adding complements to test blood, and by observing whether the complements react with antigens or antibodies in the blood and fix to the cell membranes of the antigens or antibodies, or destroy the cell membranes.
Except extremely special cases where symptoms have not been seen heretofore, and the disease is caused by a new pathogen which has not been discovered, in the treatment of diseases caused by microorganisms or the like, adequate treatment can be conducted by finding pathogens in an early stage through the microorganism test described above, and the patient can be led to recovery without worsening of the symptoms.
However, with methods such as smear, tinction, and microscopy, the detection of microorganisms is often difficult depending on their quantities, and time-consuming treatment such as the culture of specimens on an agar is required at need. Also in the virus serological test, since measurements must be performed as a rule during both the acute stage and the convalescent stage for determination from the movement of the quantities of antibodies, there is the problem of time consumption from the point of view of prompt diagnosis.
As seen in complement fixation described above, when a substance to be sensed reacts with a catching substance which catches the substance to be sensed by reacting only with specific substance to be sensed, microorganisms, the mass of the catching substance increases by the mass of the substance to be sensed, even slightly. Such an increase in the mass similarly occurs in the relationship between a catching substance and a chemical substance such as a specific gaseous substance and a smell component, and also applies to the case where a substrate itself without change in the mass is a catching substance, on which a specific substance is deposited or added. On the contrary, when a reaction in which a substance to be sensed caught by a catching substance or the like is released occurs, the mass of the catching substance or the like slightly decreases.
As an example of a method for sensing change in such a small mass, U.S. Pat. No. 4,789,804 discloses in FIG. 27 thereof a mass sensor 80 comprising a quartz oscillator 81 and electrodes 82, 83 facing the quartz oscillator. When any substance adheres externally on these electrodes 82, 83, the mass sensor 80 senses change in their mass using change in the resonant frequency of the thickness slip oscillation of the quartz oscillator 81 in the direction of the surface of the electrodes. Since such a mass sensor 80 measures change in resonant frequency basically caused by change in the mass load on the quartz oscillator 81, such a mass sensor 80 is considered to be able to be used also as a thickness meter for measuring the thickness or the growth of a vapor-deposited film, or a moisture meter.
However, when such a quartz oscillator 81 is used, since the part on which an external substance adheres and the part for detecting resonant frequency are in the same location, for example, the resonant frequency is unstable when the piezoelectric properties of the mass sensor 80 itself vary due to the temperature of the specimen or change in temperature. Also, if the specimen is a conductive solution, and when the mass sensor 80 is immersed unprotected in the specimen, a short-circuit between electrodes may occur. Therefore, the mass sensor 80 must be subjected to insulation such as resin coating.